The present exemplary embodiment relates generally to a printing system comprising at least two marking engines and, more particularly, to a scheduling system and method for use in conjunction with a printing system comprising at least two marking engines. It finds particular application in conjunction with scheduling sheets of print jobs in a multi-marking engine printing system for maximizing output of the printing system and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
In a typical xerographic marking engine, such as a copier, printer, combination copier/printer, etc., a photoconductive insulating member is charged to a substantially uniform potential and thereafter exposed to a light image representative of a document to be produced. This exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, corresponding to image areas of the document to be produced. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. This developed image may be subsequently transferred to a print medium, such as a sheet of copy paper, to which it may be permanently affixed by heating and/or by the application of pressure, i.e., fusing.
Electronic printing systems, including those that employ one or more xerographic marking engines as generally described above, can sometimes employ a scanner for scanning image-bearing documents, i.e., source documents, and conversion electronics for converting an image scanned from a source document to image signals or pixels. Alternatively, image signals or pixels representative of an image or document to be printed can be generated directly on a computer or like device, without the need for a source document. In either case, the signals are typically stored and read out successively to the printing system for formation of the images on photoconductive output media, such as a photoreceptor, and ultimately transfer to a support substrate, such as described above.
A common trend in the maintenance of office equipment, particularly copiers and printers, is to organize the printing system on a modular basis, wherein certain distinct subsystems of the printing system are bundled together into modules which can be readily removed and replaced with new modules, often of the same type. For example, the printing system could comprise two or more marking engine modules and a finisher module. Modular designed printing systems facilitate greater flexibility in terms of replacement and repair, and can even allow repairs of individual modules to take place at remote locations without necessitating disabling of the entire printing system.
Incorporated by reference, by way of background and where appropriate, are the following references relating to what have been variously called “tandem engine” printers, “cluster printing,” “output merger” and the like: U.S. Pat. No. 4,579,446; U.S. Pat. No. 4,587,532; U.S. Pat. No. 5,272,511; U.S. Pat. No. 5,568,246; U.S. Pat. No. 5,570,172; U.S. Pat. No. 5,995,721; U.S. Pat. No. 5,596,416; U.S. Pat. No. 6,402,136; U.S. patent application Ser. No. 10/785,211 by Lofthus, et al., filed Feb. 24, 2004 and entitled UNIVERSAL FLEXIBLE PLURAL PRINTER TO PLURAL FINISHER SHEET INTEGRATION SYSTEM; U.S. patent application Ser. No. 10/860,915 by Lofthus, et al., filed Jun. 3, 2004 and entitled UNIVERSAL FLEXIBLE PLURAL PRINTER TO PLURAL FINISHER SHEET INTEGRATION SYSTEM; a 1991 “Xerox Disclosure Journal” publication of November-December 1991, Vol. 16, No. 6, pp. 381-383; and the Xerox Aug. 3, 2001 “TAX” publication product announcement entitled “Cluster Printing Solution Announced.”
Printing systems employing multiple print engines often enable higher print speeds or print rates than heretofore realized by grouping a plurality of print engines together. These systems have been found to be very cost competitive and provide an additional advantage over single engine systems as a result of their inherent redundancy. For example, if one print engine fails or is unusable, the printing system is still able to function, possible at a reduced output rate, by using the remaining print engine or engines. One challenge in these systems is scheduling of print jobs and, more particularly, scheduling of individual sheets of print jobs through the various modules, including multiple modules each including a print engine, in an organized and efficient manner.
Various methods of scheduling print jobs and print media sheets of print jobs in a printing system employing multiple print engines are known. For example, U.S. Pat. No. 5,095,342 to Rarrell et al.; U.S. Pat. No 5,095,369 to Ortiz; U.S. Pat. No. 5,159,395 to Farrell; U.S. Pat. No. 5,557,367 to Yang et al.; U.S. Pat. No. 6,097,500 to Fromherz; U.S. Pat. No. 6,618,167 to Shah; 6,836,339 to Purvis et al.; and U.S. Pat. No. 6,850,336 to Purvis et al.; U.S. patent application Ser. No. 10/924,458 to Lofthus et al.; and U.S. patent application Ser. Nos. 20/384,514; 10/248,560; 10/284,561; and 10/424,322, all to Fromherz, all of which are incorporated herein in their entireties by reference., disclose exemplary scheduling systems. In particular, the '339 patent and the '336 patent disclose a scheduler for a printing machine to schedule the processing of sheets through the several modules of the printing machine.